I’ve heard it pronounced “mee-so” and “mess-o”. The joke really only works with one of them. Of course, some people get mad about a joke that involves cancer in the punchline, even if I’m making fun of Pete’s intelligence and not the disease.
At the medical office where I work, I happened to notice there was some Italian dressing in the fridge that was “best if used by” six years before. I almost felt bad throwing it out, considering it had survived at least three corporate mergers and a buy-out.